I've found that most of my pants (except for 1 pair) fall down after I run in them for a while, even if they fit me when I wear them otherwise. So I like my tights better - they keep me warmer and they stay in place. I think it's more of a preference thing. For me I want something that's light (in weight, but not warmth), stays where I want them to stay, and is a wicking material.
Are you shopping for a new pair?